INTRODUCTION: Design of a scaffold that provides mechanical strength while housing cells and growth factors is an important step to creating a physiologically sound construct. While characteristics such as elastic modulus and degradation time are material properties, architecture is a structural property and reflects the internal distribution and orientation of the scaffold material, which may play a large role in scaffold viability. It has been shown previously that cells plated on a three-dimensionally modified plate had a higher proliferative capability and gene expression compared to cells plated on a two-dimensional cell plate [1], indicating the importance of a regulated architecture in overall cellular health. Past attempts at the creation of specific micro-architecture have been relatively unsuccessful due to technological limitations. With recent advents in rapid prototyping technology, scaffolds with a regular hierarchal structure with unit sizes approximating trabecular bone pores are easily fabricated in a wide array of materials. The purpose of this study was to investigate scaffold architectures that could be fabricated with rapid prototyping and its local mechanical environment evaluated using finite element modeling.

MATERIALS AND METHODS: We designed several scaffold architectures consisting of single repeated shapes based on Archmidean and Platonic solids, including the truncated hexahedron, truncated octahedron, and rhombitruncated cuboctahedron. To evaluate the mechanical properties of these designs, we assumed a linear relationship between the properties of a single repeated unit and the entire construct. Wireframe models of the solids were generated using IronCAD (IronCAD, Atlanta, Georgia) CAD software. The shapes were modified to obtain porosity similar to normal trabecular bone (~91.5% porosity) [2]. The files were imported as .igs files into ALGOR (ALGOR Inc., Pittsburgh, PA), which was used to generate the volume mesh. All finite element analysis was completed using ALGOR for the geometric shapes. Peak stress, apparent modulus, and construct strength were evaluated.

RESULTS AND CONCLUSION: Finite element models of basic geometric constructs were successfully created using basic geometric models as foundation for the models. Three models were created: truncated octahedron, truncated hexahedron, rhombitruncated cubocatahedron. The porosity of the architecture was adjusted to match that of the average value for trabecular bone, (~91.5% porosity) obtained from the literature [2]. The shapes were chosen as they represent a micro-architecture with relatively high surface to volume ratio and a strut thickness close to the thickness of trabeculae. Current believe is that those factors most influence tissue growth on a 3-D scaffold.
The design of regulated architecture allows for the tailoring of scaffold mechanical properties, indicating a use for these scaffolds for replacing pathologic or osteoporotic bone. Current advances in rapid prototyping have paved the way to the creation of these scaffolds for growing cells inside them. Future work will include the growth of osteogenic cells in these scaffolds to evaluate tissue growth and architecture to modify mechanical properties and biological factors. The culturing of these cells will increase our knowledge of cell-environment interactions, which are extremely important in bone adaptation.

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Nanobiomaterial applications in orthopedics (PDF Download ...

Nanobiomaterial Applications in Orthopedics ... their use at load-bearing, orthopedic sites. ... As a scaffold material, ...Read more

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